A carpenter on top of a roof of 20.0m high dropped a hammer of mass 1.5kg and it fell directly to the ground. the kinetic energy of the hammer just before hitting the ground is? [g = 10 ms−²]

A. 600J
B. 150J
C. 300J
D. 450J

Correct Answer:

Option C – 300J

Explanation

K.E just before hitting the ground
= P.E at the maximum height (conservation of mechanical energy)
K.E = P.E = mgh = 1.5 x 10 x 20
= 300 J